[MITgcm-devel] background diffKr in vertical mixing pkgs

[Jean-Michel Campin]

Hi,

Regarding the background value of vertical diffusivity in pkgs:
ggl90, kl10, my82, pp81,
we currently use the temperature diffusivity (diffKrNrT)
but regarding ptracers default diffusivity (and default 3-D field diffKr), 
we use the salinity one.

I am thinking of few changes:
1) It would be more consistent to change the background value in 
   these vertical mixing schemes from diffKrNrT to diffKrNrS.
2) In addition, in the case where no vertical diffusivity for salinity is specified,
   we could change the code to use the temperature diffusivity profile 
   instead of diffKrSDefault. 
   This way, if salinity is not stepped forward (only 1 tracer), the temp. 
   diffusivity would be used as a default.

3) Regarding the implemetation of ALLOW_3D_DIFFKR in pkgs kl10, my82 & pp81
   I have the impression that the 3-D field (diffKr) is, at the end, not used
   at all (added and then substracted). Will fix this part by using
   the 3-D field diffKr as a minimum value in kl10_calc.F, my82_calc.F & pp81_calc.F
4) But in pkg ggl90 (where the background value can affect the vertical
   diffusion of TKE), I am not sure what should be done with ALLOW_3D_DIFFKR:
   continue to use diffKrNrT (or diffKrNrS) as the background ?
   or decide to use the 3-D diffKr instead ?

Comments and advise are welcome.

Cheers,
Jean-Michel